Global energy consumption is projected to significantly increase by mid-century, and this increased need may be partially met through use of renewable energy sources. Due to the intermittent nature of some of these renewable energy sources, such as wind and solar, it is desirable to incorporate compatible large-scale energy storage devices into the energy grid. Use of such grid storage is also being driven by the evolving nature of the grid (e.g., green grid, smart grid, distributed nature of the grid, etc.) as well as by other technological developments including vehicle electrification. Redox (reduction-oxidation) flow batteries, a rechargeable system that uses redox states of various species for charge/discharge purposes, represent a potential approach for grid storage.
In conventional flow batteries, electrolyte (e.g., catholyte and anolyte) that includes one or more dissolved electroactive species oftentimes flows through an electrochemical cell that reversibly converts chemical energy to electricity. The electroactive components are dissolved in a solvent rather than being in a solid state in such flow batteries. Additional electrolyte can be stored external to the cell (e.g., in tanks), and can be pumped through the cell or fed into the cell via gravity. Thus, spent electrolyte in the cell can be recovered for re-energization and replaced with electrolyte from the external tanks. While flow batteries may be charged and discharged without degradation of performance, conventional flow batteries commonly have low energy densities and include costly materials.